Post SMTP is installed. Its mailer type is SMTP, the host field reads smtp.office365.com, and the credential fields hold a mailbox address plus an app password. Contact forms, password resets, and order receipts have all flowed through that connection since the day the site went up.
At the end of December 2026, Microsoft will disable SMTP AUTH Basic Authentication by default for all Exchange Online tenants. Admins can re-enable it after that date, but Microsoft has signalled full removal in 2H 2027. The connection breaks the moment the default flips unless you act beforehand. When it does, Post SMTP’s log fills with:
550 5.7.30 Basic authentication is not supported for Client SubmissionThree paths lead out. The cost differences are large enough to name before the detail: the cheapest option costs nothing at the plugin level; the most expensive costs $99.99 a year. The table below shows where each fits. The pillar hub carries the timeline and the routing for readers on a different plugin.
Your three paths
| Path | What changes | What it costs | When it fits |
|---|---|---|---|
| A. Buy Post SMTP Pro Business tier | Microsoft 365 stays as the sender. Post SMTP stays as the plugin. The mailer switches from SMTP with a password to Microsoft Office 365 OAuth via One-Click Setup. | Post SMTP Pro Business at $99.99 a year. | Post SMTP is already on the site for a Business-tier capability, such as the mobile app’s Pro features or Microsoft Teams alerts, and the One-Click Setup comes with a tier you were going to buy anyway. |
| B. Switch to a cheaper mailer plugin | Microsoft 365 stays as the sender. Post SMTP is replaced. Either FluentSMTP (free, own Entra app) or WP Mail SMTP Pro (~$49 first year, no Entra app) takes over. | FluentSMTP: $0 at the plugin level. WPMS Pro Basic: ~$49 first year, $99 renewal. | Post SMTP was installed for reasons that no longer apply, and the Microsoft 365 mailbox as the visible From address still matters. |
| C. Switch to a transactional provider | Microsoft 365 leaves the sending path. Post SMTP stays as the plugin. A dedicated sending service takes over. | Free tiers or trials cover most WordPress-transactional volumes. | Microsoft 365 was in the stack for expedience rather than for sender identity, and you do not need the mailbox address as the visible From. |
Doing nothing is not on the table. The site stops sending; contact forms, password resets, and order receipts fail silently until fixed.
Path A: Buy Post SMTP Business tier for Microsoft One-Click OAuth
- Buy the Business tier. Post SMTP Pro Business is $99.99 a year at
postmansmtp.com/pricing. It is the only tier with Microsoft One-Click Setup; the two cheaper Pro tiers, Basic at $59.99 and Professional at $79.99, do not include it. Whether those two can connect to Microsoft 365 at all is a question Post SMTP’s own pages answer both ways. The pricing cards for both tiers list “All Pro Mailers”. The Pro install guide says any Pro bundle includes the Office 365 socket, and the setup guide for that socket has you register your own app in Azure. The comparison table on the same pricing page marks Office 365 / Microsoft 365 for Business only. We have not tested a cheaper tier, so get Post SMTP’s answer in writing before you buy one for this. Verify all three prices on the pricing page before paying; the Pro ladder has restructured before. - Install Post SMTP Pro and activate the licence. Pro is a separate add-on that runs alongside the free plugin. Download its zip from the purchase email or your postmansmtp.com account, upload it under Plugins > Add New Plugin, activate it, and paste the licence key when prompted. Then open Post SMTP > Extensions and enable both the Microsoft Office 365 extension and the Microsoft One-Click SMTP extension.
- Reconfigure the mailer. Launch Post SMTP’s Setup Wizard. Under Mailer, select “Microsoft (Outlook / Office 365)” and enable “One-Click Setup”. In the Authorization section, click “Sign in with Microsoft”, sign in as the Microsoft 365 mailbox owner, and approve the requested access. If authorization fails, a Microsoft Entra ID administrator may need to allow third-party applications or grant admin consent.
- Handle admin consent if Microsoft requires it. Accept the permissions shown during sign-in. If Microsoft reports that admin approval is required, ask a Microsoft Entra administrator for the consent that the tenant’s policy and the requested permissions call for. On reseller-provisioned Microsoft 365 tenants (GoDaddy, IONOS, hosting-bundled add-ons), the site owner may not have the required admin role. If authorization fails with
AADSTS65001, an administrator may need to grant consent before you retry. - Test and monitor. Post SMTP > Send Test Email. A successful send returns without the
5.7.30string. Watch Post SMTP > Email Log for 24 hours. A recurring5.7.30at this stage usually means a caching plugin is serving a stale settings page to an admin session that re-saves the old SMTP values on the next edit.
Path B: Switch to a cheaper mailer plugin
Two viable targets, and the choice between them comes down to whether the operator can reach Microsoft Entra.
Switch to FluentSMTP (free plugin, own Entra app)
Cost is $0 at the plugin level; the price is paid in operator time. FluentSMTP reaches Microsoft 365 OAuth by having the site owner register their own app in Microsoft Entra ID, grant it the Mail.Send Graph permission, and produce a client secret that has to be rotated before its expiry. Best fit for an operator with Global Administrator on the tenant and access to the Entra admin center.
Install FluentSMTP alongside Post SMTP and complete the FluentSMTP setup while the old plugin still handles mail. Once the new connection tests green, uninstall Post SMTP. The full Entra walkthrough is in the FluentSMTP + Microsoft 365 migration guide. Post SMTP’s Email Log does not migrate; keep Post SMTP installed for a reference window if the history matters, or accept the loss on uninstall.
Switch to WP Mail SMTP Pro (paid, no Entra app)
Cost is roughly $49 first year and $99 on renewal for the Pro Basic tier, about half the Post SMTP Business tier. WPMS’s One-Click Setup uses a centrally managed app, so no Entra app registration is required from you and there is no client-secret rotation. Best fit for an operator without a route to the Entra admin center (a reseller-provisioned Microsoft 365 tenant is the standard case) or who does not want to own the app-registration lifecycle.
Buy WPMS Pro Basic, install alongside Post SMTP, and follow the One-Click Setup in the WP Mail SMTP + Microsoft 365 migration guide. Uninstall Post SMTP once the new connection tests green. WPMS’s Debug Events log covers similar depth to Post SMTP’s Email Log. WPMS Pro’s failure alerts can reach a phone as browser push. If the reason for choosing Post SMTP was a specific Pro feature in its app, such as connecting multiple sites or resending failed emails, Path A preserves it. Post SMTP’s WordPress.org listing does not state which tier includes phone failure alerts alone.
Path C: Switch to a transactional provider
The sender identity shifts in Path C. The Microsoft 365 mailbox address leaves the From field; a subdomain of your domain (typically send.example.com) takes its place. For contact forms, password resets, and order receipts, this distinction is invisible to recipients. It only matters when recipients expect to reply to the Microsoft 365 mailbox and that inbox isn’t forwarding replies onward. If sender identity doesn’t matter, this path drops the tenant-admin coordination step entirely.
Post SMTP ships native mailers for Postmark, SMTP2GO, Mailgun, and SendGrid in the free plugin. Only the mailer selection and credentials change.
- Pick the provider. Postmark leads on deliverability for pure transactional mail; its free plan allows 100 emails/month for testing, deliverability evaluation, and low-volume side projects, and Postmark says it never expires. SMTP2GO is 1,000 emails a month free with no stated expiry, good for mixed transactional and light marketing. Mailgun‘s free plan, also with no stated expiry, is 100 emails a day; it makes sense when other Mailgun infrastructure is already in the stack. SendGrid runs a 60-day trial at 100 emails a day; after that it is paid from $19.95 a month, with no permanent free tier. The SMTP plugins roundup runs the full comparison.
- Provision the domain. Sign up, verify the domain, and publish the SPF and DKIM records the provider issues. Sending from the mailbox address itself is possible but breaks Microsoft 365’s inbound reply routing unless the mailbox forwards those replies onward.
- Reconfigure Post SMTP. Post SMTP > Settings > Account. Change the mailer type from “SMTP” to the provider (all four ship in the free plugin), paste the API key or SMTP credentials from the provider dashboard, and Send Test Email. Same 24-hour monitoring window as the other paths.
- Retire the Microsoft 365 SMTP AUTH configuration. In the mailbox owner’s account portal, under Security > App passwords, revoke the app password the site was using. If tenant policy allows, an Exchange admin can also disable SMTP AUTH on the mailbox with
Set-CASMailbox -SmtpClientAuthenticationDisabled $true. Both are optional but tidy.
Which path when
Take Path A when a Business-tier capability, such as the mobile app’s Pro features or Microsoft Teams alerts, is the reason the site is on Post SMTP. At $99.99 a year the Microsoft One-Click is a reasonable incremental line item on a tier the site was going to buy anyway, not a defensible standalone purchase.
Take Path B when Post SMTP is on the site for reasons that no longer apply (came pre-installed with a theme, or a previous admin picked it in a hurry) and the Microsoft 365 mailbox as the visible From address still matters. FluentSMTP is the answer with Entra access; WPMS Pro Basic is the answer without. Neither costs what Post SMTP Business does.
Take Path C when Microsoft 365 was in the stack for expedience rather than for sender identity. Transactional providers deliver contact-form notifications and order receipts more reliably than a repurposed mailbox does, and the available free tiers cover most WordPress-transactional volumes. A meaningful share of Post SMTP plus Microsoft 365 readers will find Path C is the answer they had been avoiding.
When none of the paths fit
If Post SMTP is on the site for its mobile-app alerting, there is no route to Global Administrator, and the Business tier is out of budget: Path C plus Post SMTP’s provider-side webhook notifications may cover the failure-notification job; the WordPress.org listing does not state the tier or cost for mobile-app alerts. The trade is the Microsoft 365 mailbox as the visible sender address.
If the site is on Microsoft 365 SMTP relay via connector (port 25 with an IP allowlist), or on Direct Send, the SMTP AUTH retirement does not apply and this is the wrong migration. Microsoft 365 SMTP relay and Direct Send covers those configurations.
Related
- Microsoft 365 is disabling password SMTP is the pillar hub; if you landed here from a search and are not sure which plugin you have, start there.
- WordPress SMTP with Microsoft 365 covers the evergreen OAuth setup for readers starting fresh rather than migrating.
- Post SMTP review has the full Pro-tier breakdown for readers weighing whether the Business tier is worth it for their site.
- Microsoft 365 as a WordPress SMTP server is for readers reconsidering whether Microsoft 365 should stay in the sending path at all.
- Gmail and Yahoo bulk-sender rules for WordPress is the companion pillar for sites that cross the 5,000-a-day Gmail threshold; the authentication work applies on any of the three paths above.
Corrections
- 2026-11-09: an earlier version called Mailgun’s free plan permanent. Mailgun’s current Free-plan listing gives 100 emails/day but does not state an expiry.
- 2026-11-05: an earlier version said WP Mail SMTP did not cover mobile failure alerts. WP Mail SMTP’s documentation shows browser-based push alerts on mobile devices, a Pro feature.
- 2026-11-05: an earlier version implied Post SMTP’s mobile-app failure alerts need the Business tier. That tier includes the app’s Pro features, and Post SMTP’s WordPress.org listing marks multi-site monitoring and resend as Pro, not the alerts.
- 2026-11-05: an earlier version said Post SMTP’s Business tier is the one that includes Microsoft 365 OAuth, that Pro needs no separate install, that One-Click starts under Settings > Account, and that it always needs tenant admin consent. Business is the only tier with One-Click Setup, and Post SMTP’s pages disagree on whether its cheaper tiers include the Office 365 connection. Pro is a separate add-on whose extensions you enable, One-Click starts in the Setup Wizard, and an administrator may need to grant consent if authorization fails.